Method of drilling a hole for printed wiring board

Abstract: A method of drilling a through-hole for inter-surface conduction in a laminate for a printed wiring board, the laminate comprising a metal foil attached to an insulating material, with a water-soluble lubricant sheet on one surface or on front and reverse sides of the laminate, the method comprising drilling the through-holes in the presence of a water-soluble lubricant sheet which is 0.02 to 3 mm thick and is formed from a mixture of 20 to 90 % by weight of a polyether ester with 10 to 80 % by weight of a water-soluble lubricant.

Description: The present invention relates to a metbod of drilling a through-hole for a double-sided or multilayered printed wiring board. US-A-4,781,495 and US-A-4,929,370 disclose methods of drilling a hole for inter-surface conduction in a laminate produced by attaching a metal foil on an insulating material, with a water-soluble lubricant placed on one surface, or front and reverse sides, of the laminate. It is disclosed that these methods use a sheet prepared by impregnating paper, etc., with a mixture of a glycol such as diethylene glycol or dipropylene glycol, which is a solid water-soluble lubricant, with a rigid wax such as fatty acid or a nonionic surfactant. As a wax-like hardener component, a fatty acid ester can be used. However, the problem of the above methods is that the effect on the prevention of heat generation in a drill is insufficient, that a porous sheet is only poorly impregnated with the above mixture or that the sheet is sticking. JP-A-4-92488 to JP-A-4-92493 disclose methods of drilling a hole in a laminate with a specific water-soluble lubricant placed on the laminate. It is disclosed that in these methods the water-soluble lubricant is selected from polyethylene glycol having a weight average molecular weight of 600 to 9,000, monoether of polyoxyethylene, ester of polyoxyethylene, monoester of polyoxyethylene sorbitan and a polyoxyethylene-propylene block copolymer. These methods show some improvement, while the effect on the prevention of heat generation in a drill is not satisfactory. Further, JP-A-4-92494 discloses a water-soluble lubricant sheet which is 0.05 to 3 mm thick and is formed from 20 to 90 % by weight of a polyethylene glycol having a weight average molecular weight of at least 10,000 and 80 to 10 % by weight of a water-soluble lubricant. The above water-soluble lubricant sheet shows a sufficient improvement in the effect on the prevention of heat generation in a drill, while the defect with this sheet is that it is liable to break so that it is difficult to handle it. It is an object of the present invention to provide a method of drilling a through-hole for a printed wiring board, in which the heat generation in a drill bit can be inhibited in drilling holes and quality holes can be highly efficiently made. It is another object of the present invention to provide a method of drilling a through-hole for a printed wiring board, in which quality holes can be highly efficiently made in the presence of a novel water-soluble lubricant sheet which has high strength and can be handled easily. According to the present invention, there is provided a method of drilling a through-hole for inter-surface conduction in a laminate comprising a metal foil attached to an insulating material, in the presence of a water-soluble lubricant sheet on the front and/or reverse side(s) of the laminate, wherein the water-soluble lubricant sheet is 0.02 to 3 mm thick and is formed from a mixture of 20 to 90 % by weight of a polyether ester with 10 to 80 % by weight of a water-soluble lubricant. The laminate produced by attaching a metal foil to an insulating material, referred to in the present invention, is a material produced by integrating a metal foil and an insulating material and used for producing a printed wiring board. The above laminate includes a metal-clad laminate, a multilayered laminate having a printed wiring in an internal layer, a multilayered, metal-clad laminate having a printed wiring in an internal layer and a metal-clad plastic film. The polyether ester used in the present invention is a water-soluble resin obtained by reacting a glycol or ethylene oxide such as polyethylene oxide, polypropylene glycol, polytetramethylene glycol, polypropylene oxide or a copolymer of at least two of these with phthalic acid, isophthalic acid, terephthalic acid, sebacic acid, dimethyl ester of any one of these, diethyl ester of any one of these, a polyhydric alcohol such as trimellitic acid or an anhydride or ester thereof. The melting point of the polyether ester is preferably in the range of from 30 to 200°C, particularly preferably in the range of from 35 to 150°C. The water-soluble lubricant used in the present invention is typically selected from at least one of polyethylene glycols having a weight average molecular weight of 600 to 9,000, polyoxyethylene monoethers, polyoxyethylene esters, polyoxyethylene sorbitan monoesters, polyglycerin monostearates and polyoxyethylene-propylene block copolymers. Suitable polyoxyethylene monoethers include polyoxyethylene oleyl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene dodecyl ether, polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether. Suitable esters of polyoxyethylenes include polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate and polyoxyethylene beef tallow fatty acid ester. Suitable monoesters of polyoxyethylene sorbitans include polyoxyethylene sorbitan monostearate. Suitable polyglycerin monostearates include hexaglycerin monostearate and decaglycerin monostearates. The melting point or softening point of the water-soluble lubricant is preferably in the range of from 30 to 200°C, particularly preferably in the range of from 40 to 150°C. The sheet having a thickness of 0.02 to 3 mm is produced from a mixture of 20 to 90 % by weight of the above polyether ester and 80 to 10 % by weight of the above water-soluble lubricant, and this sheet is used as a water-soluble lubricant sheet. When the amount of the water-soluble lubricant is too large, undesirably, it is difficult to produce a sheet from the mixture. When it is too small, undesirably, the sheet shows insufficient lubricity. The method for producing the above water-soluble lubricant sheet is not specially limited. For example, the water-soluble lubricant sheet is produced by a method in which the above polyether ester and the water-soluble lubricant are homogeneously mixed with a roll, a kneader or other kneading means under heat as required to prepare a homogeneous mixture and the mixture is extruded, press-processed or roll-processed to form a sheet having a thickness of 0.02 to 3 mm. The sheet is placed on at least one plastic or metal foil surface of the laminate when used for drilling a hole in the laminate. When the water-soluble lubricant sheet used in the present invention is placed on one surface, it is preferred to place the sheet so that the sheet is on a drill bit side. The water-soluble lubricant sheet is also preferably used by attaching it to an aluminum foil used as a material in drilling a hole, with an adhesive. Examples The present invention will be explained hereinafter with reference to Examples. Examples 1 - 9 A polycondensate (trade name; PAOGEN PP-15 or Paogene EP-15, supplied by Dai-ichi Seiyaku Kogyo Co., Ltd.) from polyethylene glycol and dimethyl terephthalate was used as the polyether ester (to be referred to as PEES hereinafter). PEES and a water-soluble lubricant in amounts shown in Table 1 were kneaded at a temperature of 80 to 120°C (in N 2 gas), and then the mixture was extruded with an extruder to form a sheet having a thickness of 0.2 mm. Holes were drilled in 1.6 mm thick glass epoxy six-layered laminate (four inner layers, inner layer copper foil thickness 70 µm, outer layer copper foil thickness 18 µm) under the following conditions. [Conditions for drilling holes] Drill bit 0.35 mm in diameter Revolution number 80,000 rpm Feed rate 1.6 m/min Number of laminates 2 [Arrangement] (viewed from the drill bit side) Water-soluble lubricant sheet 100 µm thick aluminum foil Six-layered laminate Six-layered laminate Paper phenol laminate The above-obtained water-soluble lubricant sheet was evaluated for tensile strength, solubility in water and occurrence of smear, and further, the six-layered laminate were evaluated for a pink ring. Table 1 shows the results. Comparative Example 1 Holes were made in the same manner as in Example 1 except that the arrangement changed as follows without using the water-soluble lubricant sheet. Table 1 shows the results. (Drill bit side) 100 µm aluminum foil Six-layered laminate Six-layered laminate Paper phenol laminate Comparative Example 2 A sheet having a thickness of 0.2 mm was obtained from 40 parts by weight of a polyoxyethylene oxide having a weight average molecular weight of 160,000 (to be referred to as PO hereinafter) and 60 parts by weight of polyoxyethylene monostearate by kneading and extruding them in the same manner as in Example 1. The resultant sheet was evaluated in the same manner as in Example 1. Table 1 shows the results. Example 10 A sheet having a thickness of 0.2 mm was obtained from 20 parts by weight of a polyethylene glycol·dimethyl terephthalate condensate (trade name; PAOGEN PP-15, supplied by Dai-ichi Kogyo Yakuhin Co., Ltd.), 20 parts by weight of polyethylene oxide (trade name; ALCOX R-150, supplied by Meisei Chemical Co., Ltd.) and 60 parts by weight of polyoxyethylene monostearate by kneading and extruding them in the same manner as in Example 1. The resultant sheet was evaluated in the same manner as in Example 1. Table 1 shows the results. The abbreviations used in Table 1 stand for the following. *1: Water-soluble lubricants LEG1 = Polyethylene glycol having a weight average molecular weight of 1,000 LEG2 = Polyoxyethylene lauryl ether having a weight average molecular weight of 1,100. LEG3 = Polyoxyethylene monostearate having a weight average molecular weight of 3,300 LEG4 = Polyoxyethylene sorbitan monostearate having a weight average molecular weight of 1,300 LEG5 = Hexaglycerin monostearate having a weight average molecular weight of 530 LEG6 = Polyoxyethylene-propylene block copolymer having a weight average molecular weight of 8,800 LEG7 = Polyethylene glycol having a weight average molecular weight of 4,000 *2: Occurrence of smear after 4,000 bits A wall of a through-hole was measured for an area in which the inner copper layer was exposed, i.e. a degree of adherence of a resin, by observing it with a microscope. The degree of occurrence of a smear was rated as follows: 100 % exposure of copper = 10, 50 % exposure of copper = 5, no exposure of copper = 0. Specifically, 4,000 through-holes were drilled with a drill bit, and then 20 through-holes were drilled. The walls of these 20 through-holes were measured to obtain an average. In the column of "Occurrence of smear after 4,000 bits" in Table 1, the parenthesized data shows the smallest copper exposure area among the 20 through-holes. *3: After drilled, two six-layered boards were immersed in a 4N HCl aqueous solution at 25°C for 5 minutes, and a length of corrosion with 4N HCl from the through-hole wall was measured on each of the boards. A smear and a pink ring prevent a contact between a plated through-hole and an electrically conductive layer formed on an insulating material, and the degrees of occurrence of these constitute an important standard for the evaluation of quality of printed wiring board. *4: A sheet-shaped test piece having a width of 10 mm and a length of 100 mm was placed in water having a temperature of 40°C so that the half of the test piece was perpendicularly immersed 50 mm deep in the water, and a time was counted until the test pieces was dissolved, broken and fallen in a portion contacting the water surface. Components for sheet Tensile strength (kg/mm 2 ) After 4,000 bits Solubility in water*4 (second) PEES PO Water-soluble lubircant*1 Occurrence of smear*2 Pink ring*3 PP-15 EP-15 kind part Ex.1 40 - - LEG1 60 0.80 9.4(9.0) 200 µm 50 Ex.2 40 - - LEG2 60 0.75 9.5(9.0) 200 µm 50 Ex.3 40 - - LEG3 60 0.75 9.5(9.1) 200 µm 50 Ex.4 40 - - LEG4 60 0.70 9.3(9.0) 200 µm 50 Ex.5 40 - - LEG5 60 0.70 9.4(8.9) 200 µm 50 Ex.6 40 - - LEG6 60 0.75 9.4(8.9) 200 µm 50 Ex.7 40 - - LEG7 60 0.75 9.4(9.0) 200 µm 50 Ex.8 - 40 - LEG3 60 0.70 9.4(9.0) 200 µm 50 Ex.9 70 - - LEG3 30 1.25 9.2(8.8) 250 µm 60 Ex.10 20 - 20 LEG3 60 0.50 9.5(9.0) 200 µm 40 CEx.1 - - - - - - 8.5(4.0) 500 µm - CEx.2 - - 40 LEG3 60 0.30 9.5(8.9) 200 µm 60 The water-soluble lubricant sheet, used in the present invention, has high strength and can be handled easily. The method using the above water-soluble lubricant sheet serves to drill a quality hole in a laminate with high efficiency, and therefore has high performance in practical use in industry.

Claims: A method of drilling a through-hole for inter-surface conduction in a laminate, the laminate comprising a metal foil attached to an insulating material, in the presence of a water-soluble lubricant sheet on the front and/or reverse side(s) of the laminate, wherein the water-soluble lubricant sheet is 0.02 to 3 mm thick and is formed from a mixture of 20 to 90 % by weight of a polyether ester with 10 to 80 % by weight of a water-soluble lubricant. A method according to claim 1, wherein the water-soluble lubricant is selected from at least one of polyethylene glycols having a weight average molecular weight of 600 to 9,000, polyoxyethylene monoethers, polyoxyethylene esters, polyoxyethylene sorbitan monoesters, polyglycerin monostearates, and polyoxyethylene-propylene block copolymers. A method according to claims 1 or 2, wherein the polyether ester has a melting point or softening point of 30 to 200°C. A method according to any preceding claim, wherein the water-soluble lubricant has a melting point or softening point of 30 to 200°C.

Inventors: EJIRI MITSUO, KINBARA HIDENORI, EJIRI, MITSUO, KINBARA, HIDENORI, EJIRI, MITSUO, C/O MITSUBISHI GAS CHEM. CO., INC., KINBARA, HIDENORI, C/O MITSUBISHI GAS CHEM. CO.,
Applicants: MITSUBISHI GAS CHEMICAL CO, MITSUBISHI GAS CHEMICAL COMPANY, INC.
Application year: 1994
Main classification: H05K3
IPC codes: H05K3, B23B41, B23Q11, B26F1, B23B35